1. FIELD OF THE INVENTION
This invention relates to an optical recording medium for recording data by using an optical method and method for manufacturing the same.
2. DISCUSSION OF RELATED ART
There are known optical recording medium made by laminating a recording layer on the top of the surface of a preformat pattern of a transferred layer, wherein the transferred layer of the preformat pattern made of organic compound is adhered on one side of a transparent substrate.
FIG. 13 is a cross-sectional view of the layered structure of an optical disc as an embodiment of the optical recording medium, which is the subject of the present invention, wherein transferred layer 2 of the preformat pattern formed on one side of the transparent substrate 1 is made of, a first organic compound layer 3 comprised of a curing resin such as, for example a photo curing resin or the like and, a second organic compound layer 4 comprised of a material such as, for example, cellulose nitrate or the like, and recording layer 5 is laminated on the surface of the second organic compound layer 4.
Also, as a method for manufacturing such an optical recording medium, there is known a method of transferring the reversed pattern (preformat pattern) of a signal patterned surface formed on a stamper on the first and the second organic compound by the method of applying uniformly the second organic compound, which is the base of the second organic compound layer 4, and forming a film on the signal patterned surface of a mold for medium manufacturing, which is called a stamper, placing the first organic compound which is the base of the first organic compound layer 3 on top of the second organic compound and pressing the transparent substrate 1 to the first organic compound to expand it to a uniform thickness.
This method has the advantage of being able to improve the recording-reproducing characteristics because it is able to make the thickness of the second organic compound layer uniform, and also it does not change the shape of the preformat pattern, in comparison with the method comprising transferring of the preformat pattern on the single layer of the first organic compound layer, and subsequent spin coating of the second organic compound layer on its patterned surface.
As for the stamper, there are known stampers made of metal or resin, but for reason of better endurance and so on, a stamper made of metal (for example, nickel) is generally used. Also, as for the second organic compound, there are used polymers such as cellulose nitrate, polyvinyl alcohol, polyvinyl alcohol nitride, polytetrafluoroethylene, guanine, and polymers similar to these polymers formed by plasma polymerization.
However, when using the metal stamper and an organic compound comprising the second organic layer 4 which has a large adhesion strength, the exfoliating process has to be done slowly and carefully. Otherwise, it is liable to cause exfoliation at the interface of the first organic compound layer and the second organic compound layer, and it is accordingly difficult to manufacture a good replica with good efficiency. Also, a large exfoliating force is needed to separate the replica from the stamper, therefore inconveniences such as deformation of the transferred preformat pattern or, in the worst case, breakage of the transparent substrate and ripping of the replica layer due to its partial sticking to the stamper, or the like is liable to occur.